Effects of wind erosion on the spatial heterogeneity of soil nutrients in two desert grassland communities

Wind is known to affect the spatial heterogeneity of soil resources in arid and semiarid systems, but multi-year, quantified observations are largely absent. We studied the effects of wind erosion on the spatial distribution of soil organic carbon (SOC) and other soil nutrients at the Jornada Experimental Range, in southern New Mexico. Enhanced wind erosion was encouraged by grass cover reduction in a Sporobolus-mesquite dominated site (SM) and a Bouteloua-mesquite dominated site (BM). The scale and magnitude of spatial dependence for the soil analytes were quantified using geostatistical analyses. Results of this study show that soil organic matter related analytes such as SOC, TN, N_avail, and SO₄ ^2- are among the first to be eroded and redistributed; cations such as Ca²⁺ and Mg²⁺ may not be removed and redistributed significantly; and other ions such as K⁺, Na⁺ and Cl⁻ showed no discernible pattern of change. Geostatistics show that wind appeared to increase the scale of spatial autocorrelation, but decrease the scale of spatial dependence of most soil analytes over 2–3 windy seasons. In the wind enhanced plot of the SM site, up to 99% of the spatial dependence of SOC was autocorrelated at the distance of 1.45 m before the initiation of wind erosion, but the spatial dependence dropped significantly to only 60% at a larger autocorrelation distance of 2.76 m after three windy seasons. Similar but less significant changes were observed for SOC in the BM site. Despite the differential effects of wind on the soil analytes, we conclude that the overall results of wind on the grass cover reduction plots are the disappearance of small, strong fertile islands, which may be related to grasses; and the reinforcement of large fertile islands, which are likely related to mesquite shrubs. In addition, the change of the spatial patterns of SOC and other soil nutrients induced by enhanced wind erosion may persist and reinforce soil islands associated with shrubs, thus allowing a positive feedback for further desertification in this arid grassland.     

Ecosystem Restoration of Jhum Fallows in Northeast India: Microbial C and N Along Altitudinal and Successional Gradients

Abstract To characterize the altitudinal and successional trends in microbial biomass and to understand their role in soil nutrient dynamics during the aggradation phase (vegetation recovery) of abandoned shifting cultivation systems, we determined the soil properties and microbial C and N in jhum (slash‐and‐burn) cultivation systems at different altitudes and 1‐, 7‐, and 16‐year‐old fallow agricultural lands at lower and higher altitudes in the northeastern Indian hills. Density of ground vegetation was lower in the undisturbed forest than in the jhum fallows. In general, 1‐year jhum fallow had greater herbaceous vegetation both at lower and higher altitudes. Although woody plants were observed in 7‐ and 16‐year‐old jhum fallows, their density was highest in the forest. Soil moisture, organic C, and total N also increased gradually with increasing altitude and progressive secondary succession. Soil pH showed a negative correlation with altitude (as also confounded by soil type) and fallow age. Both microbial C and N had a close correlation with altitude and fallow age. Contribution of microbial C to soil organic C was 2.0–2.6% and microbial N to total N 1.4–2.2% in jhum fields, 2.4–4.3% and 1.2–2.1%, respectively, in jhum fallows, and 2.5–2.9% and 1.6–1.9% in the forests. Microbial C and N showed a negative correlation with herbaceous plant density. Microbial biomass in the jhum fallows and forest stands had a positive relationship with woody vegetation. Along an altitudinal and/or successional gradient, microbial C and N were positively correlated with water‐holding capacity, soil moisture, organic C, and total N and negatively correlated with soil pH. Microbial C and N were positively correlated with each other. Therefore, the study suggests that the altitudinal and successional dynamics of microbial C and N are linked to, among other properties, soil organic matter and total nitrogen contents in the soil during community development after land abandonment from shifting cultivation.     

Woody species and nutrient accumulation during the fallow period of milpa farming in Belize,C.A.

Plant lifeform composition and levels of nutrients accumulated by fallows aged 1, 2 and 3 years under shifting (milpa) cultivation in Belize were measured. Levels of N, P and K allocated to leaves rapidly reached a plateau in 1 year old fallows with little increase in 2 and 3 year old sites. In stem material, K was accumulated rapidly, with little increase after the first year of fallow growth, while N and P accumulation proceeded at steady rates during three years of fallow development. Total biomass in 3 year old fallows averaged 2070 g m^–2 with 10.3 g m^–2 N, 0.73 g m^–2P and 13.2 g m^–2K. Nutrient concentrations in early successional species were higher than in species of later successional status, suggesting different strategies for nutrient utilization.Woody lifeforms dominated the fallow vegetation, accounting for 80% of total biomass in first year fallows and eliminating herbaceous species after 2 and 3 years of fallow growth. The importance of rapid recovery of woody species is discussed as it relates to fallow management and weed control.     

喀斯特常绿落叶阔叶混交林土壤磷钾养分空间异质性

在木论国家级自然保护区内喀斯特常绿落叶阔叶混交林内建立500 m×500 m长期监测样地,采用经典统计学和地统计学方法研究喀斯特森林土壤磷钾养分含量及其空间变异特征。结果表明:研究区土壤全磷(TP)、全钾(TK)、速效磷(AP)、速效钾(AK)含量分别为(1.60±0.76)g/kg、(5.42±2.74)g/kg、(5.74±3.63)mg/kg、(5.20±2.96)mg/kg;磷钾养分含量均为中等变异,变异强度为APAKTKTP。研究区土壤TP、TK、AP、AK变异函数值的最佳拟合模型均为指数模型,决定系数均很高(0.671-0.995),TP、AP呈中等强度空间自相关,TK、AK呈弱空间自相关。TP、AP的变程较长,分别为336.00 m和373.50 m,空间连续性较好,TK、AK变程较短(33.30 m、64.50 m),空间依赖性较强。土壤TP表现为坡下(含洼地)含量高,坡上含量较低;AK表现为坡中含量高于洼地含量;AP、TK呈斑块破碎化分布。海拔、坡度和地面凹凸度是土壤磷钾养分空间异质性的主要影响因素。喀斯特常绿落叶阔叶混交林土壤磷钾养分存在不同空间异质性和空间关联性,这为小流域尺度上土壤养分管理、可持续利用策略、喀斯特退化生态系统生态恢复提供理论依据。     

Spatial Heterogeneity and Soil Nitrogen Dynamics in a Burned Black Spruce Forest Stand: Distinct Controls at Different Scales

We evaluated spatial patterns of soil N and C mineralization, microbial community composition (phospholipid fatty acids), and local site characteristics (plant/forest floor cover, soil pH, soil %C and %N) in a 0.25-ha burned black spruce forest stand in interior Alaska. Results indicated that factors governing soil N and C mineralization varied at two different scales. In situ net N mineralization was autocorrelated with microbial community composition at relatively broad scales (∼ ∼8 m) and with local site characteristics (`site' axis 1 of non-metric scaling ordination) at relatively fine scales (2–4 m). At the scale of the individual core, soil moisture was the best predictor of in situ net N mineralization and laboratory C mineralization, explaining between 47 and 67% of the variation (p < 0.001). Ordination of microbial lipid data showed that bacteria were more common in severely burned microsites, whereas fungi were more common in low fire severity microsites. We conclude that C and N mineralization rates in this burned black spruce stand were related to different variables depending on the scale of analysis, suggesting the importance of considering multiple scales of variability among key drivers of C and N transformations.     

Nutrient stocks in managed and natural humid tropical fallows

Managed fallows which recover nutrients more rapidly than natural secondary vegetation may improve the performance of shifting agriculture systems operating under inadequately long fallow cycles. Our objective was to construct nutrient balances for the soil, vegetation, and litter compartments of six planted leguminous fallows and natural secondary vegetation during 53 months. The fallows were planted on a previously cultivated Ultisol (Acrisol) in the Peruvian Amazon and included:Centrosema macrocarpum (Centrosema),Pueraria phaseoloides (Pueraria),Stylosanthes guianensis (Stylosanthes),Desmodium ovalifolium (Desmodium),Cajanus cajan (Cajanus), andInga edulis (Inga). In addition, in the natural fallow treatment secondary vegetation was allowed to establish and grow naturally. Quantities of extractable P, K, Ca, and Mg, total N, and organic C in soil to a 45 cm depth, and macrouttrients in aboveground biomass, roots, and litter were estimated at fallow planting, at 8, 17, and 29 months afterward, and at fallow clearing (53 months). Total N stocks increased by 10% in the Stylosanthes, Desmodium, Pueraria, and Inga treatments, but changed little in the Cajanus, Centrosema and natural fallows. This difference was largely due to greater net increases in both soil and vegetation compartments in the former group of treatments. In the Inga, Desmodium, and natural fallows, total stocks of P and K at 53 months were about 40% to 80% greater and 12% greater, respectively, than initial values, but Ca and Mg stocks were reduced by 25% to 40%. In the other treatments, there was generally little change in P stocks, but large (30% to 60%) reductions in K, Ca, and Mg during the course of the fallow. Although there were net decreases of stocks of P, K, Ca, and Mg in soil in all treatments during the fallow, storage of P and K in vegetation and litter in the Inga, Desmodium, and natural fallows offset losses of these nutrients from soil. These treatments also tended to accumulate more Ca and Mg in biomass and litter than the other treatments. These results suggest that leguminous fallow vegetation that accumulates large amounts of biomass may increase N, P, and K stocks, but that incomplete recuperation of Ca and Mg may limit the sustainability of short-rotation fallow-based systems on acidic, infertile soils. ei]Section editor: G R Stewart     

Variation in soil seed bank species composition of a dry coniferous forest: spatial scale and sampling considerations

In order to assess the effects of disturbance on soil seed bank spatial structure, variation in seed bank species composition was analyzed at two spatial scales in mature (undisturbed) and recently disturbed stands of Interior Douglas-fir forest in south-central British Columbia. Coarse-scale analysis among stands 10–100 km apart using Multi-Response Permutation Procedures showed that individual mature stands were mainly characterized by unique seed bank species compositions. Disturbance had an homogenizing effect on seed bank species composition at the coarse scale––there was less variability among stands following disturbance by both low and high severity fires, and by non-salvage logging. In contrast, finer scale analysis among sampling units c. 10 m apart showed that heterogeneity in seed bank species composition was greater on severely burned and logged sites, commensurate with greater levels of soil disturbance, than on lightly burned and undisturbed sites. Despite the high intensity of seed bank sampling (sixty 25 cm² soil samples from each of 16 sites), species-area curves leveled off only when infrequent species were removed from the dataset. The number of seed bank samples required to account for the common species ranged from 84 on severely burned sites, to 196 on undisturbed sites; more than the 240 samples collected per disturbance class in this study would have been required to account for the remaining infrequent species. Overall, this study highlights the importance of sampling intensively within multiple stands to capture the variation in species composition inherent to these dry coniferous forest soil seed banks.     

喀斯特森林土壤养分的空间异质性及其对树种分布的影响

以贵州省茂兰国家级自然保护区喀斯特峰丛坡面中原生性常绿落叶阔叶混交林为研究对象, 以建立的100 m × 100 m样地的群落学调查数据和基于网格取样的土壤养分数据为基础, 采用半方差函数、Kriging空间插值和典范对应分析(canonical correspondence analysis, CCA)等方法分析了喀斯特森林土壤养分的空间异质性特征及其对树种分布的影响。结果表明: 喀斯特峰丛坡面土壤养分的变异系数为10%-80%, 变异程度中等。各土壤养分指标均具有良好的空间自相关性, 其中全磷(TP)、全钾(TK)、全镁(TMg)和pH值呈强烈的空间自相关, 而有机质(OM)、全钙(TCa)、速效磷(AP)和速效钾(AK)为中等程度的空间自相关; TCa的空间变异尺度最小, OM、TP和AK的空间变异尺度较大。土壤TK、TP、TCa、TMg、AP和pH值等随着海拔高度的增加和岩石裸露率的降低而逐渐减少, OM则随着海拔高度的增加而趋于增加, 这表明喀斯特地形因子是造成土壤养分空间变异的重要因素。CCA分析表明, 土壤养分的空间变异性显著影响到群落中树种的组成与空间分布, 其中TK、TMg、pH值、TCa和OM的影响最为明显, 体现了不同植物在土壤资源利用上的生态位分化, 这有助于喀斯特森林群落物种多样性与稳定性的维持。     

两个林分水曲柳土壤种子库空间格局的定量比较

依据地统计理论和方法,采取规则网格数据结构的空间取样设计,在树种组成、林分密度及林下植被等均不相同的两个林分中设置样地,对水曲柳土壤种子库的空间格局进行了定量比较研究．结果表明,在水曲柳杨树等混生的样地1,种子库密度较大(158．1±96．7个·m^-2),异质性程度较高(C0+C＝0．549),格局尺度相对较大(4．52m),空间自相关因素引起的变异高达89．4％,随机变异仅占10．6％,格局变异呈现较高的自相似性(分数维值D＝1．728-1．865)．在水曲柳纯林中的样地2,种子库密度较小(57．4±44．7个·m^-2),异质性程度较低(C0+C＝0．125),且主要体现在相对较小的尺度范围内(2．59m),空间自相关变异占56．8％,随机因素对空间格局的影响较大(D＝1．906-1．960)．两样地之间种子库空间格局表现的尺度范围、强度及空间结构等有显著差异,林分空间异质性是导致这种差异的主要原因．     

Carbon, nitrogen and phosphorus in volcanic soils following afforestation with native birch (Betula pubescens) and introduced larch (Larix sibirica) in Iceland

Afforestation has become an important tool for soil protection and land reclamation in Iceland. Nevertheless, the harsh climate and degraded soils are growth-limiting for trees, and little is know about changes in soil nutrients in maturing forests planted on the volcanic soils. In the present chronosequence study, changes in C, N and total P in soil (0–10 and 10–20 cm depth) and C and N in foliar tissue were investigated in stands of native Downy birch (Betula pubescens Enrh.) and the in Iceland introduced Siberian larch (Larix sibirica Ledeb.). The forest stands were between 14 and 97 years old and were established on heath land that had been treeless for centuries. Soils were Andosols derived from basaltic material and rhyolitic volcanic ash. A significant effect of tree species was only found for the N content in foliar tissue. Foliar N concentrations were significantly higher and foliar C/N ratios significantly lower in larch needles than in birch leaves. There was no effect of stand age. Changes in soil C and the soil nutrient status with time after afforestation were little significant. Soil C concentrations in 0–10 cm depth in forest stands older than 30 years were significantly higher than in heath land and forest stands younger than 30 years. This was attributed to a slow accumulation of organic matter. Soil N concentrations and soil P_tot were not affected by stand age. Nutrient pools in the two soil layers were calculated for an average weight of soil material (400 Mg soil ha⁻¹ in 0–10 cm depth and 600 Mg soil ha⁻¹ in 10–20 cm depth, respectively). Soil nutrient pools did not change significantly with time. Soil C pools were in average 23.6 Mg ha⁻¹ in the upper soil layer and 16.9 Mg ha⁻¹ in the lower soil layer. The highest annual increase in soil C under forest compared to heath land was 0.23 Mg C ha⁻¹ year⁻¹ in 0–10 cm depth calculated for the 53-year-old larch stand. Soil N pools were in average 1.0 Mg N ha⁻¹ in both soil layers and did not decrease with time despite a low N deposition and the uptake and accumulation of N in biomass of the growing trees. Soil P_tot pools were in average 220 and 320 kg P ha⁻¹ in the upper and lower soil layer, respectively. It was assumed that mycorrhizal fungi present in the stands had an influence on the availability of N and P to the trees. Responsible Editor: Hans Lambers.     

Bird diversity and endemism along a land‐use gradient in Madagascar: The conservation value of vanilla agroforests

Land‐use change is the most important driver of biodiversity loss worldwide and particularly so in the tropics, where natural habitats are transformed into large‐scale monocultures or heterogeneous landscape mosaics of largely unknown conservation value. Using birds as an indicator taxon, we evaluated the conservation value of a landscape mosaic in northeastern Madagascar, a biodiversity hotspot and the center of global vanilla production. We assessed bird species richness and composition by conducting point counts across seven prevalent land‐use types (forest‐ and fallow‐derived vanilla agroforests, woody and herbaceous fallow that are part of a shifting cultivation system, rice paddy, forest fragment and contiguous old‐growth forest). We find that old‐growth forest had the highest species richness, driven by a high share of endemics. Species richness and community composition in forest‐derived vanilla agroforest were similar to forest fragment, whereas fallow‐derived vanilla agroforest was most comparable to woody fallow. The open land‐use types herbaceous fallow and rice paddy had fewest species. Across forest fragments, vanilla agroforests, and woody fallows, endemic bird species richness was positively correlated to landscape‐scale forest cover. We conclude that both fallow‐ and forest‐derived vanilla agroforests play an important but contrasting role for bird conservation: Fallow‐derived agroforests are less valuable but take fallow land out of the shifting cultivation cycle, possibly preventing further degradation. Conversely, forest‐derived agroforests contribute to forest degradation but may avoid total loss of tree cover from forest fragments. Considering the land‐use history of agroforests may thus be a promising avenue for future research beyond the case of vanilla. Abstract in Malagasay is available with online material     

传统农业生态系统中桤木改良土壤效应研究综述

桤木(Alnus nepalensis)是一种重要的非豆科固氮植物,广泛分布于喜马拉雅山脉东部地区。在东南亚地区的传统农业生态系统中,多用桤木作为休耕树种,或将其与农作物间作。桤木根瘤固氮量随季节和年龄而变化,在桤木-小豆蔻(Elettaria cardamomum)系统中15年达到高峰(155 kg·hm^-2);桤木通过共生固氮对系统产生的氮增加量在纯桤木林中7年达到高峰(117 kg·hm^-2)。桤木与农作物间作可显著提高农作物的产量,桤木-小豆蔻立地上小豆蔻的经济产量是在森林-小豆蔻立地上的2.2倍。桤木休闲地的休闲效果明显好于自然休闲地,其地上部分生物量在休闲6年后是自然休闲地的4倍,N蓄积量是自然休闲地的3倍,P、K蓄积量是自然休闲地的2倍。桤木根系特征似乎最适合混农林系统,其细根生物量(FRB)集中于土壤剖面上层10 cm范围内,在此范围内,FRB在“树+农作物”间作条件下比在“只有树”条件下高5%;在两种立地条件下,60%以上的细根都分布于树干周围0.5 m内,大部分木质根(直径>0.5 mm)都分布于土壤上层0~10 cm处,长度都不超过1 m。桤木可加速系统的养分循环。桤木凋落物降解速率比非固氮植物快,并且与其它植物凋落物混合后的降解速率与自身凋落物降解速率一样快。在传统刀耕火种系统中,用桤木替代自然林休闲在3~6年内即可恢复土壤肥力,改善土壤理化性质,显著缩短休闲周期。该文综述了近30年来桤木在传统农业生态系统中改良土壤效应的研究成果,以提高人们对桤木的生态作用的重视程度,使人们更好地将桤木利用到农业生态系统中,达到发展山区农业和保护生态环境双赢的目的。     

广西森林土壤主要养分的空间异质性

通过对广西区7大森林片区的11个主要森林类型样地土壤养分含量进行分析,利用地统计学方法,研究了广西区森林主要土壤养分的空间变异状况及分布格局,探讨了其相关的生态学过程,以期为广西区森林分区与林间采取不同措施管理提供科学依据。结果表明:广西区森林土壤主要养分基本属于中等变异,速效养分变异大于全量养分,其中AP、AK变异程度最大;广西森林土壤主要养分的半变异函数均表现出一定的空间结构特征,TN、TP、AP表现为中等强度的空间自相关,TK、AN、AK表现为强烈的空间自相关;不同土壤养分空间结构不同,Kriging等值线图表明广西区氮素含量比较丰富、K含量中等、P含量较少,北部片区土壤养分含量普遍大于南部片区,这可能与气候、降雨、人工种植森林树种、地形、林地管理措施等有关。     

No evidence of spatial root system segregation and elevated fine root biomass in multi-species temperate broad-leaved forests

Differences in spatial rooting patterns among coexisting species have been recognized as an important mechanism for generating biodiversity effects on ecosystem functioning. However, it is not yet clear whether complementarity in root space exploration is a universal characteristic of multi-species woody communities. In a temperate broad-leaved forest with a mosaic of species-poor and species-rich stands, we tested two hypotheses related to putative below-ground ‘overyielding’ in more diverse forests, (1) that species mixture results in a partial spatial segregation of the fine root systems of different species, and (2) that stand fine root biomass increases with tree species diversity. We investigated 12 stands either with one, three, or five dominant tree species (4 replicate stands each) under similar soil and climate conditions for stand fine root biomass and spatial root segregation in vertical and horizontal direction in the soil. Fine roots of different tree species were identified using a morphological key based on differences in colour, periderm surface structure, and branching patterns. In species-poor and species-rich stands, and in all tree species present, fine root density (biomass per soil volume) decreased exponentially with soil depth at very similar rates. Stand fine root biomass in the densely rooted upper soil (0–40 cm depth) was not significantly different between stands with 1, 3 or 5 dominant tree species. We conclude that ‘below-ground overyielding’ in terms of higher fine root biomasses in species-rich stands as compared to monospecific ones does not occur in these broad-leaved forests which most likely results from a missing complementarity in vertical rooting patterns of the present tree species.     

Structure of the Microbial Communities in Coniferous Forest Soils in Relation to Site Fertility and Stand Development Stage

Abstract The structure, biomass, and activity of the microbial community in the humus layer of boreal coniferous forest stands of different fertility were studied. The Scots pine dominated CT (Calluna vulgaris type) represented the lowest fertility, while VT (Vaccinium vitis-idaéa type), MT (Vaccinium myrtillus type), and OMT (Oxalis acetocella–Vaccinium myrtillus type) following this order, were more fertile types. The microbial community was studied more closely by sampling a succession gradient (from a treeless area to a 180-years-old Norway spruce stand) at the MT type site. The phospholipid fatty acid (PLFA) analysis revealed a gradual shift in the structure of the microbial community along the fertility gradient even though the total microbial biomass and respiration rate remained unchanged. The relative abundance of fungi decreased and that of bacteria increased with increasing fertility. The structure of the bacterial community also changed along the fertility gradient. Irrespective of a decrease in fungal biomass and change in bacterial community structure after clear-cutting, the PLFA analysis did not show strong differences in the microbial communities in the stands of different age growing on the MT type site. The spatial variation in the structure of the microbial community was studied at a MT type site. Semivariograms indicated that the bacterial biomass, the ratio between the fungal and bacterial biomasses, and the relative amount of PLFA 16:1ω5 were spatially autocorrelated within distances around 3 to 4 m. The total microbial and fungal biomasses were autocorrelated only up to 1 m. The spatial distribution of the humus microbial community was correlated mainly with the location of the trees, and consequently, with the forest floor vegetation. Received: 9 November 1998; Accepted: 26 April 1999     

格氏栲天然林土壤养分空间异质性

采用地统计学与GIS技术相结合方法对格氏栲天然林土壤养分和pH值空间异质性进行了研究,结果表明:pH值为弱变异,土壤养分为中等变异,变异强度为有效磷＞速效钾＞水解性氮＞全氮＞全钾＞全磷＞pH值.半方差最优模型拟合分析表明,pH值、全钾、有效磷符合指数模型,全氮符合高斯模型,全磷、水解性氮符合球状模型,速效钾符合线状模型;全钾、速效钾、pH、全氮、全磷、水解性氮和有效磷的有效变程依次为1806、549、267、130、120、182 m和117m;从空间结构特征看,pH值、全氮、全磷、水解性氮、有效磷表现出强烈的空间自相关,其空间异质性主要受结构性因素影响;全钾具有中等强度的空间自相关,其空间异质性是随机性因素和结构性因素共同作用的结果;速效钾具有微弱的空间自相关,其空间异质性主要受随机性因素影响.土壤养分空间分布特征:全氮、全磷由南向北递增;全钾含量呈环状分布,向南北分别呈递增趋势;pH值由东北到西南递增,呈条带状分布;水解性氮从东北向西南递减;有效磷从东南到西北逐渐递增;速效钾分布较均匀,在西北和东南角各有一个高值区,从西南到东北表现为先增加后减少的规律.其结果为区域尺度上土壤养分的空间内插、制图和取样设计提供参考,也为土壤可持续利用、格氏栲天然林的恢复与重建提供科学依据.     

Cultivated and fallow fields harbor distinct communities of Basidiomycota

Basidiomycota constitute a group of fungi with highly diverse ecological strategies from ectomycorrhizas and plant pathogens to saprotrophic fungi. We used 454 sequencing to obtain sequences of Basidiomycota from a cultivated and an adjacent fallow field, to investigate the influence of soil cultivation on the species composition and distribution patterns. Nonparametric multidimensional scaling (NMS) clearly segregated the basidiomycetes communities in the two fields, though some species were shared. Axis 1 and 2 of the ordination correlated with soil organic matter content and pH respectively. Most OTUs had affinity to known species, but some unknown clades were seen in both fields. Spatial analysis demonstrated higher spatial autocorrelation (up to 50 m) in the managed field in comparison with the fallow field. The study showed that agricultural soils have considerable species richness, and that community composition and turn-over potentially is influenced both by land use and spatial scale.     

The effect of fallow and continuous cultivation on the chemical and physical properties of an alfisol in western Nigeria

Summary Soil properties under continuous cropping were compared with those under planted fallows and natural bush regrowth for three years after forest clearing. The cropping treatments consisted of continuous maize with and without stover returned as surface mulch, continuous soybean, and maize and cassava intercropped. The fallow treatments included pigeon pea, leucaena, Guinea grass and natural bush regrowth.In the continuous soybean and unmulched maize plots, soil organic matter and pH declined rapidly; whereas the mulched maize plots maintained a soil organic matter level comparable to the fallow treatments. To maintain soil organic matter in the surface soil at a level comparable to soil under secondary forest, two to three applications of a total amount of 16 MT/ha/annum of dry plant materials (maize stover or grass) are required when the material is applied as surface mulch.In the cropped plots, favorable physical characteristics in the surface soil were also maintained when sufficient plant residue was returned; whereas the deterioration of subsoil structure of the forest soil occurred in all cropping treatments.Guinea grass fallow has a distinct advantage in recycling mineral nutrients and maintaining soil physical properties and organic matter. It is suggested that soils may be planted with a combination of Guinea grass and pigeon pea fallow for one or two years after three or four years of arable cultivation.IITA Journal Paper No. 65 IITA Journal Paper No. 65     

Intermediary disturbance increases tree diversity in riverine forest of southern Brazil

Floods are frequently associated with disturbance in structuring riverine forests and they lead to environmental heterogeneity over space and time. We evaluated the distribution of tree species, ecological groups, species richness and diversity from the point bar to the slope of a riverside forest in southern Brazil (Lat. 30°01′S, Long. 52°47′W) to analyze the effects of flooding on soil properties and forest structure. A plot of 50 × 200 m divided in five contiguous transects of 10 × 200 m parallel to the river was installed, where we measured all the individual trees with pbh ≥ 15 cm. A detailed topographical and soil survey was carried out across the plot and indicated significant differences in organic matter and most mineral nutrients through the topographical gradient. The 1,229 surveyed individuals belonged to 72 species and 35 families. We used Partial CCA and Species Indicator Analysis to observe the spatial distribution of species. Both analyses showed that species distribution was strongly related to the flooding gradient, soil properties and also by space and pure spatial structuring of species and environmental variables (spatial autocorrelation), although a large part of variation remains unexplained. The ecological groups of forest stratification, plant dispersal and requirements for germination indicated slight differences among frequently, occasional and non-flooded transects. Species richness and diversity were higher at intermediate elevations and were associated to the increased spatial–temporal environmental heterogeneity. Across the plot, the direct influence of flooding on tree species distribution created a vegetation zonation that is determined by predicted ecological traits.     

Development processes and growth pattern of Pinus densiflora stands in central eastern Korea

Stand growth and developmental processes were investigated in Pinus densiflora Siebold et Zucc. stands of different ages in the central eastern region of Korea. Stands were inventoried and five trees per stand were sampled for stem analysis, age estimation, and growth analysis. More than 80% of sampled trees in a stand were established within 3–5 years, and most stands had a single cohort structure. The initial growth of pine seedlings was slow, but the height growth accelerated beyond 2–3 m height, 5–10 years after establishment. Linear growth was maintained until 10–12 m height, at which suppressed trees fell behind and might die out. The young stand was composed of pure pines, while few pine seedlings and saplings were found in the understory of older stands. The peak of diameter growth rate occurred around 5–15 years after tree establishment, implying that competition begins during that period. The pine stand development follows four stages: (1) the young stage when the growth rate increases and peaks; (2) the height competition stage when trees focus on height growth for light while maintaining a narrow DBH and height distribution; (3) the differentiation stage when suppressed trees die out, and the DBH distribution becomes wider; and (4) the mature stage when stands have a multi-canopy structure with a wide DBH and height distribution, while the understory is dominated by other tree species. The changes in growth rates and stand structure through forest development would be implemented to predict alterations of above-ground carbon sequestration rates.